A gate valve is used, for example, in a processing apparatus that performs processing such as etching using a radical of fluorine (F) or oxygen (O) on a workpiece such as a semiconductor wafer or a liquid crystal substrate in a process chamber that is evacuated and into which process gas is introduced, and has a role in opening the gate opening when the workpiece is carried in and out of the chamber and hermetically closing the gate opening during the processing in the chamber. In general, this type of gate valve is configured such that a seal member such as an O-ring is attached in an annular dovetail groove formed in a valve plate, and the gate opening is opened and closed by bringing the seal member into and out of contact with a valve seat provided around the gate opening.
Now, it is known that if, in a gate valve having such a configuration, radicals generated in a hermetically closed chamber during processing act on the seal member through a gap between the valve plate and a side wall in which the gate opening is provided, the deterioration of the seal member is hastened, and particles are generated. Attempts to suppress the deterioration of the seal member due to radicals include PTL 1 and PTL 2.
On the other hand, in order to achieve more reliable sealing of the gate opening, measures to more reliably prevent the seal member from coming off a dovetail groove are also desirable.